People are generally aware of the most common causes of hallucinations, like schizophrenia and a really high fever. But lesser known are the more rare causes; here are six you probably haven't heard about.

Autism spectrum disorder (ASD) is detected in children who suffer from qualitative impairments of social reciprocity and communication, along with restricted and repetitive behaviors. These autistic traits are more commonly reported in boys than girls, and research has yet to fully explore the reasons. According to a recent study, girls may be underdiagnosed and underserved with ASD because of their ability to outperform boys when it comes to recognizing social cues in familiar situations.

The Autism Society says that while there is no known single cause for ASD, it is generally accepted that it's caused by abnormalities in brain function or its structure. The difficulty autistic children have with forming facial expressions during social situations may be the result of physiological problems with areas of the brain that control facial nerves. Boys are four to five times more likely to be diagnosed with ASD than girls. The disparity in ASD diagnosis in gender could lend to the possibility of genetic differences between the sexes. Criteria for ASD diagnosis is based primarily on male behavior, but girls may just be better at hiding these particular traits.

Researchers from the University College London sought to investigate the association between autistic traits and emotion recognition using facial and social motion cues in males and females. Using participants from the Avon Longitudinal Study of Parents and Children (ALSPAC), 3,666 children were assessed on their ability to accurately identify emotions using the faces of the Diagnostic Analysis of Non-Verbal Accuracy and the Emotional Triangles Task. These tests measure recognition of emotion from social motion cues. The children with autistic-like traits were compared to children who did not display such difficulties.

The cohort of children were asked to perform a series of two tests to measure their autistic traits. In the first test, the participants were shown photographs of children expressing happiness, sadness, anger, or fear. Errors and misattributions were associated with higher scores on this test. The second test was a computerized task, which measured the participants' ability to identify emotional mental states during five-second animations consisting of a triangle and circle moving around a screen. In 20 of the animations, the triangle moved around in ways that portrayed happiness, sadness, anger, and being scared. In another four animations, the triangles moved in a manner that appeared inanimate or “not living,” according to a Bristol University news release.

The findings showed both boys and girls who were previously identified as having autistic traits — based on a questionnaire about social communication completed by their parents — were more likely to make errors when identifying sad and scared faces, and more likely to mistakenly recognize faces as happy. However, when they looked at both genders separately, girls were better at recognizing emotions in the photographs but performed poorly with the triangle cartoons. This revelation suggests girls may be better at masking ASD signs in typical social situations but are less likely to do so in unfamiliar situations.

“The lack of association between social communication difficulties and facial emotion recognition in girls suggests girls might learn to compensate for facial emotion recognition difficulties,” said Dr. Radha Kothari, lead author of the study, in the news release.

The current assessment of clinical ASD in girls may need to be reevaluated as the findings suggest a call for a gender-specific assessment of ASD traits and characteristics to understand the causes of the disorder and provide better individual treatment for both genders, respectively.

A similar study found that 7- to 9-year-old boys were six times more likely than girls to be diagnosed with ASD by their teachers. However, when both a teacher and a parent completed the Autism Spectrum Screening Questionnaire (ASSQ), there was a 2.1 to 1 male to female ratio. This finding suggests that there is an assumption that boys are more likely to have the condition than girls, which may lead to an underdiagnosis in girls.

Females with ASD who may be underdiagnosed may retreat to a period of extreme loneliness and confusion. They may be at an increased risk of depression since girls are less likely to display ASD traits, such as concern, aggression, or language delay until puberty, says autismhelp.info. Autistic girls tend to have rigid attitudes and behaviors, and a tendency to be very self-focused which can leave them susceptible to suffer from extreme weight gains or losses, or to develop eating disorders such as anorexia.

It is imperative to improve ASD criteria diagnosis as the findings of these studies suggest many girls may be missing out on key treatment and therapy, which leaves them vulnerable to developing other health complications later in life.

To learn how to identify autistic characteristics in children, click here.